A conventional electronic circuit device has a voltage comparator circuit that compares a signal voltage of an input signal with a given voltage that is determined based on a power supply potential to output a comparison result. This circuit device may be used, for example, as a temperature sensor circuit as disclosed in JP 9-88708A. In this temperature sensor circuit, a change in a resistance due to the temperature of an exhaust gas temperature sensor is detected as a change in the voltage, input to a comparator, and compared with a given reference voltage. As a result, it is possible to determine whether the temperature detected by the exhaust gas temperature sensor exceeds a given set temperature or not.
Specifically, in this temperature sensor circuit, a voltage at a common connection point between an exhaust gas temperature sensor and a voltage division resistor circuit is input to an inverting input terminal of the comparator of a comparator circuit through a resistor. Also, a voltage at the common connection point between resistors which are connected in series between a power supply terminal and a ground terminal is input to a non-inverting input terminal of the comparator as a reference voltage.
Here, this temperature sensor circuit may be integrated into an electronic control unit (ECU) that is mounted in a vehicle, the drive electric power is generally supplied from a battery device provided in the vehicle. The ECU is connected to the battery device through a current limit resistor used as a protective resistor so that, even when a high voltage is applied directly to the ECU from a power generation device such as an alternator in a state where the battery device is disconnected from the ECU, a large current does not flow in the ECU. As a result, this current limit resistor causes a voltage drop.
For example, as shown in FIG. 8, an electronic circuit device 100 may be designed as an integrated circuit and has a signal processor circuit 102 and a voltage comparator circuit 104. The signal processor circuit 102 subjects an input signal Sig1 input from an input terminal IN1 to given signal processing to output a processed signal to an output terminal OUT1. The voltage comparator circuit 104 compares an input signal Sig2 input from an input terminal IN2 with a threshold voltage Vth to output a comparison result to an output terminal OUT2. Those circuits 102 and 104 are incorporated into an ECU. The ECU is connected to a battery device Batt through a current limit resistor R7. As a result, a supply voltage Vcc that is supplied to the electronic circuit device 100 becomes a value (Vcc=VB−ΔV) obtained by subtracting a voltage drop ΔV developed by the current limit resistor R7 from a terminal voltage VB of the battery device Batt.
The voltage drop ΔV is a product of a current Icc that flows in the electronic circuit device 100 and a resistance of the current limit resistor R7. A consumption current I1 of the signal processor circuit 102 varies according to a signal voltage level of the input signal Sig1. Therefore, even if a consumption current (I2+I3) of the voltage comparator circuit 104 is stabilized or do not vary, it is difficult to suppress a variation of the voltage drop ΔV due to the current limit resistor R7. The variation in the voltage drop ΔV directly affects a reference voltage source Vref that provides the threshold voltage Vth of the voltage comparator circuit 104. Therefore, the variation in the voltage drop ΔV directly leads to a variation in the threshold voltage Vth that is a comparison reference of the voltage comparator circuit 104, and the comparison determination of the input signal Sig2 due to the comparator CP1 may become inaccurate.